Normally, food passes easily from the stomach into the duodenum (the first part of the small intestine) through a valve called the pylorus. In pyloric stenosis, the muscles of the pylorus are thickened. This thickening prevents the stomach from emptying into the small intestine.

The cause of the thickening is unknown, although genetic factors may play a role. Children of parents who had pyloric stenosis are more likely to have this problem.

Pyloric stenosis occurs more often in boys than in girls, and is rare in children older than 6 months. The condition is usually diagnosed by the time a child is 6 months old.

Symptoms

Vomiting is the first symptom in most children:

Vomiting may occur after every feeding or only after some feedings

Vomiting usually starts around 3 weeks of age, but may start any time between 1 week and 5 months of age

Vomiting is forceful (projectile vomiting)

The infant is hungry after vomiting and wants to feed again

Other symptoms generally appear several weeks after birth and may include:

Abdominal pain

Belching

Constant hunger

Dehydration (gets worse with the severity of the vomiting)

Failure to gain weight or weight loss

Wave-like motion of the abdomen shortly after feeding and just before vomiting occurs

Signs and tests

The condition is usually diagnosed before the baby is 6 months old.

A physical exam may reveal signs of dehydration. The infant may have a swollen belly. The doctor may detect the abnormal pylorus, which feels like an olive-shaped mass, when touching the stomach area.

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